1. Field of the Invention
The present invention relates to a jig for forming a sealant layer for a lightning protection fastener used in an airframe of an aircraft, and more particularly, used in a wing.
2. Description of the Related Art
In general, a wing constituting an airframe of an aircraft has a hollow structure. A wing panel forming a wing surface is fixed to a structural member inside of the wing by a fastener member.
The fastener member fastens the wing panel to the structural member by inserting a pin-shaped fastener body into through holes respectively formed in the wing panel and the structural member inside the wing from outside of the wing, and fixing a distal end portion of the fastener body by using a fixture such as a collar and a nut from inside of the wing.
A structural member other than the wing panel, a member for fixing accessories or the like are also fastened and fixed by the fastener member inside the wing or a fuselage portion.
In aircrafts, all possible lightning protection measures need to be taken by giving lightning protection capability to the fastener member.
That is, when aircrafts are struck by lightning and high current flows through the wing panel and the structural member of a main wing or the like, the high current partly or, in some cases, entirely flows through a fastened portion fastened by the fastener member including the fastener body and the fixture. If the current has a value exceeding a limit value of passage allowable current in each fastened portion, electric discharge called electric arc (or thermal spark) occurs (the electric discharge is referred to as arc below in the present specification). This is a phenomenon in which a rapid temperature rise occurs in a fastened interface between members mainly made of a conductive material and constituting the fastened portion due to the current passing through the fastened portion, thereby causing the members to locally melt, and electric discharge to occur in the surrounding atmosphere. In many cases, high-temperature melts called hot particles scatter from the melting portion.
An inner space of the wing generally doubles as a fuel tank. It is thus necessary to take explosion protection measures on the fuel tank so as to prepare for lightning strikes. When the above arc or hot particles have energy exceeding a certain level, the arc or hot particles could ignite fuel vapor in the fuel tank. Therefore, in the lightning strikes, by taking double redundant measures of (1) suppressing the occurrence of arc in the fastened portion, and (2) sealing the arc, the arc discharge needs to be prevented from occurring, and the hot particles scattering therefrom need to be prevented from contacting the flammable fuel vapor to thereby prevent ignition. Here, examples of a portion where the flammable fuel vapor possibly exists include an inner portion of the fuel tank inside the wing and inside the fuselage portion, an inner portion of a surge tank (where a vent scoop, a burst disk or the like are placed) generally placed on a wing tip side of the fuel tank, and an inner portion of fuel-system accessories. To prevent the occurrence of arc in the fastened portion, bonding is performed so as to improve electrical conductivity between the fastener member and the structural member. Surface bonding is performed in a case of high current. Fastener bonding is performed (a conductive fastener is used as the fastener) when the current has a value within a medium region. A metal fastener may be simply used in a case of low current.
As a method for sealing the arc, a configuration in which a cap made of an insulating material is attached so as to cover a required portion of a fastener member, and an inner portion of the cap is filled with a sealant so as to fill a gap between the fastener member and the cap has been proposed (e.g., Japanese Patent Laid-Open No. 2010-254287). However, when the cap is mounted, a fastener portion for mounting is required. It is thus necessary to extend the length of a fastener body. Since a great number of fastener members are provided in an aircraft, the weight of the aircraft is increased. Fuel consumption is thereby deteriorated.
When the fastener member is attached to a narrow portion with a small space therearound, a space for mounting the cap may not be ensured.
A method for ensuring lightning protection capability by overlaying an insulating sealant layer on a fastener member without attaching the cap has been also applied. However, workers form the sealant layer based on visual observation. It is thus not easy to accurately form the sealant layer having a required thickness for ensuring the lightning protection capability around the fastener member.
In view of the above problems, a main object of the present invention is to provide a jig for forming a sealant layer for a lightning protection fastener which enables to quickly and accurately form a sealant layer having a required thickness around a fastener member.